Linesman's telephone

[Welsh Anorak]

Hi everyone
I have to admit I know little about telephones so I need to know about a "TMC Linesman's Telephone 704" I've just bought. It looks as new in a smart green case. It was apparently used to test ISDN lines for broadcasting (I think!) and has a couple of XLR sockets attached but otherwise is original. So how does it work? What can I do with it?
Forgive my ignorance!
Glyn

[peter_sol]

Probably modified by the BBC with its XLR's
But google Linesman 704 and there is all the info including circuit diagram.

[Dave Moll]

Yes, I was wondering about the XLRs. Mine simply has the connectors that either take 4mm plugs or screw onto wire/spade terminals.

I connect a lead going to a BT master socket into which I can plug telephones to test (on the "LB" setting of the 704). It also includes a ring current generator by moving the switch from "LB" to "ring".

[russell_w_b]

Originally Posted by Welsh Anorak

So how does it work? What can I do with it?
Forgive my ignorance!
Glyn

It's a very useful piece of kit to have around. It will run as an automatic or CB telephone (Central Battery), connecting (using BT socket wires 3 & 5) to the PSTN network.

But it is really useful when testing old telephones, as it will run as a LB (Local Battery) telephone as well! Not only that, but it has a built-in transmission bridge such that connection to any telephone (746, 706, 332, etc...) will enable full two-way speech, without the need for batteries, other than the three 'D'-cells in your 704.

In LB mode, you can run it, in conjunction with another LB telephone, as a point-to-point telephone system.

Your 704 will provide a 25Hz rough ringing current from a transistorised inverter within, at about 50V RMS, useful for testing bells on telephones. It's easier to do this by connecting an old ADSL filter or master-LJU box to the terminals (or, in your case, XLR sockets), so that you can plug in the telephone under test directly.

If you're into pimping old telephones, the 704 is arguably one of the most useful tools in your armoury.

[FIXITNOW]

i have just picked up one of these (704)sadly no longer in its green case
as some one has rehoused it in an old homemade box
but it was only a pound

[AndiiT]

Hi,
I agree that these are very useful to have around, I am fortunate enough to have a couple of these in my collection, one with a dial and one without.
Strangely the transmitter cut - off button on one of the units works the opposite way around to the other one!
i.e you have to depress (and hold in) the button to speak.

Regards
Andrew

[russell_w_b]

Originally Posted by AndiiT

Strangely the transmitter cut - off button on one of the units works the opposite way around to the other one!
i.e you have to depress (and hold in) the button to speak.

Same on one of our Works 704s - a TMC manufactured one. It may be a 704B model - I'll have a better look tomorrow. Up until now I thought someone had been playing around and had modified it!

[JCM3000]

A great bit of kit, especially as it takes standard batteries!